Preprints  

Dosimetric dating methods based on the analysis of luminescence signals emitted by granular minerals extracted from sedimentary deposits now play an important role in the study of the Quaternary. Here we propose a new approach in which the age of the deposit is calculated by combining the equivalent dose and dose rate distributions. The underlying Bayesian mathematical model and its implementation via an R code are provided, together with the results obtained for a finite set of configurations.

When first introduced together with the depth profile technique to determine the surface exposure age, the linear inversion approach has suffered with the drawbacks of not incorporating erosion and muons into calculation. In this paper, we increase the accuracy and applicability of linear inversion approach by fully considering surface erosion, muogenic production, and radioactive decay, while maintain its advantage of being straightforward to apply to determine an exposure age.

We present a record of ice retreat from the northern Alexander Archipelago, Alaska. During the last Ice Age (~26,000–19,000 years ago), these islands were covered by the Cordilleran Ice Sheet. We tested whether islands were ice free during the last Ice Age for human migrants moving from Asia to the Americas. We found that these islands became ice-free between ~15,100 years ago and ~16,000 years ago, and thus these islands were not suitable for human habitation during the last Ice Age.

Cosmogenic nuclides are now widely applied in the Earth sciences, however more recent applications often push the analytical limits of the technique. Our study presents a comprehensive method for analysis of cosmogenic ¹⁰Be and ²⁶Al samples down to isotope concentrations of few thousand atoms per gram of sample, which opens the door to new and more varied applications of cosmogenic nuclide analysis.

It is of critical importance to dosimetric dating techniques that the quantity of the radiation dose is estimated accurately. Here we describe instruments, measurement procedures and data analyses required for estimating parent nuclide activities. We describe analytical procedures required to generate data with sufficient accuracy and precision for samples in secular equilibrium and illustrate additional procedures to quantify disequilibrium.

We used cosmogenic radionuclides in detrital river sediment to measure physical erosion rates of watersheds in central Cuba; erosion rates are lower than chemical denudation rates in lowland watersheds. Data from two different cosmogenic nuclides suggest that some basins may have a deeper than typically modeled mixed layer and could have experienced significantly burial after or during exposure. We conclude that significant mass loss may occur at depth through chemical weathering processes.

Multi-thermochronometry, in which methods such as (U-Th)/He dating of zircon and apatite, and apatite fission-track dating are combined, is used to reconstruct rock thermal histories. Our ability to reconstruct thermal histories and interpret the geological significance of measured ages requires modeling. Here we use forward models to explore grain size and chemistry effects on cooling ages and closure temperatures for the (U-Th)/He decay systems in apatite and zircon.

Fission tracks are damage trails from uranium fission in minerals, whose thermal histories are deduced from their number and length. A mineral is etched for observing the tracks with a microscope. We show that the etching and observation conditions affect the track count and explain it in the framework of a recent etch model. We conclude that established solutions do not secure that the ages and thermal histories inferred from track counts and measurements are accurate.

Calcite is frequently formed during alteration processes in the basaltic, uppermost layer of juvenile oceanic crust. Weathered oceanic basalts are hard to date with conventional radiometric methods. We show in a case study from the North Pamir, Central Asia, that calcite U-Pb age data – supported by geochemistry and petrological microscopy – has the potential to date sufficiently old oceanic basalts, if the time span between basalt extrusion and latest calcite precipitation (~ 25 Ma) is considered.

This paper outlines a method that helps mineral explore for gold. When can see the alteration caused by the mineralising fluids, it is possible to use geochemical methods to vector towards the deposit. But such methods failed at Martabe. We decided to work out why. Our results showed that there were several distinct and separate very short-lived alteration events. The answer might be that vectoring is possible only when samples are compared from the same mineralising system.

This study presents erosion rates of the George River and seven of its tributaries in northeast Tasmania, Australia. These erosion rates are the first measures of landscape change over millennial timescales for Tasmania. We demonstrate that erosion is closely linked to a topographic rainfall gradient across George River. Our findings may be useful for efforts to restore ecological health to Georges Bay by determining a pre-disturbance level of erosion and sediment delivery to this estuary.

We develop in-situ produced terrestrial cosmogenic krypton as a new tool to date and quantify Earth surface processes; the motivation being the availability of six stable and one radioactive isotope (⁸¹Kr, half-life 229 kyr) and of an extremely weathering-resistant target mineral (zircon). We provide proof of principle that terrestrial Kr_it can be quantified and used to unravel Earth surface processes.

Phanerozoic sedimentary rocks of northern Canada have compositionally heterogeneous detrital apatite with high age dispersion caused by differential thermal annealing. Discrete AFT kinetic populations with variable annealing temperatures are defined using elemental data but are poorly resolved using conventional parameters (D_par and Cl). Inverse thermal modelling of samples from northern Yukon reveals a complicated record of multiple heating-cooling cycles consistent with geological constraints.

We present a 3100 year annually banded lake mud record, with an error of −13/+7 %, representing more undercounting than overcounting. Our results provide realistic sedimentation rates that can be used to calculate flux. Our method expands the possibility to overcome the obstacles of indistinct or interrupted banding that can affect the quality and amount of information about environmental change and age. Our results provide realistic sedimentation rates that can be used to calculate flux.

The µDose-system is an innovative analytical instrument developed for the cost- and time-efficient determination of environmental radionuclide concentrations required for the calculation of sedimentation ages in palaeo-environmental and geo-archaeological research. The results of our study suggest that accuracy and precision of µDose-measurements are comparable to those of well-established methods and that the new approach shows the potential to become a standard tool in environmental dosimetry.

Paleomagnetic data from Cascade Lake (Brooks Range, Alaska) extend the radiometric-based age model of the sedimentary sequence extending back 21 kyr. Correlated ages based on prominent features in paleomagnetic secular variations (PSV) diverge from the radiometric ages in the upper 1.6 m, by up to about 2000 years at around 4 ka. Four late Holocene cryptotephra in this section support the PSV chronology and suggest the influence of hard water or aged organic material.

Subarctic/Arctic lake sediments provide key data to understand natural climate variability and future climate change, but are difficult to date and of limited use without a robust chronology. A ~21,000 year climate record from Cascade Lake (Alaska) has divergent age models based on two dating methods. We resolve this using volcanic ash deposits; proving paleosecular variation is a viable dating technique in the region, reporting new ash isochrons, and providing a reconciled Bayesian age model.

Levinson-Lessing Lake in northern central Siberia provides an exceptional archive for the evolution of the Earth's magnetic field in the Arctic. This is the first palaeomagnetic study carried out at the lake and presents the relative palaeointensity and palaeosecular variation of the upper 38 m of sediment core Co1401, spanning ~62 ka. A comparable high-resolution record of this time does not exist in the Eurasian Arctic.

Mineral grains within sediment or rock absorb a radiation dose from the decay of radionuclides in the host matrix. For the beta dose component, the estimated dose rate must be adjusted for the attenuation of beta particles within the mineral grains. We show here that the mean dose rate to dosimeter grains in a granular matrix is dependent on the grain-size distributions of the source grains, and of the bulk sediment, as well as on the grain size of the dosimeters.

This research is part of a Ph.D thesis examining evaporite detachments characteristics. ⁴⁰Ar/³⁹Ar geochronology is employed to constrain the timing of formation and deformation events. A diagenetic age of 514 ± 3 Ma is interpreted from the oldest significant step age. Other step ages may represent a Cambrian-Permian deformation event or a complex mixing age of diagenetic Ar with partially reset Ar during the Cenozoic. We report the first closure temperature for polyhalite between 281 and 296 °C.

Prehistoric volcanic eruptions are often dated by wiggle matching series of radiocarbon ages on tree rings to standard calibration curves, ignoring potential contamination by 'old' carbon given off by the volcano. We modeled the effects of low amounts of contamination on wiggle match dates for the 10th century Changbaishan eruption and found evidence of contamination in all. We propose a new protocol to identify the presence of contamination, and provide more secure dates for major eruptions.

When using trapped-charge dating methods to determine the time of deposition of a sediment, it is of great importance to know whether the signal containing the age information, has been completely erased before burial or if a residual signal is inherited. We examined the residual doses of the quartz ESR signals of young fluvial sediments from the lower Rhine terraces with known luminescence ages. We found varying but large residuals indicating an incomplete bleaching of the quartz ESR signals.

Fission tracks are generated in minerals due to spontaneous fission of U-238. The initial track length decreases with time due to recrystallization. The age of a track can be calculated by counting the number per volume of the shorter tracks and include the decay constant. However, the theoretical order of track length versus time is disrupted by uncertainties. We have shown how the order can be reestablished. It is then possible to determine the age of tectonic events such as uplift or burial.

Cooling ages date the time at which minerals cross a certain isotherm on the way up to Earth's surface. Such ages can be measured from bedrock material as well as from river sand. If spatial variations of bedrock ages are known in a river catchment, the spatial distribution of erosion can be inferred from the distribution of the ages measured from the river sand grains. Here we develop a new tool to help such analyses, with particular emphasis on quantifying uncertainties due to sample size.

A novel technique for the uranium-lead dating of geologically young carbonates is described and tested. The technique expands our ability to date geological events such as fault movements and past climate records.

The timing and duration of fluid activity within a gold deposit enables a greater understanding of how the deposit evolved and thus help future mineral exploration. This research uses high resolution dating methods to unravel the overprinting fluid activity at the Martabe gold field in Sumatra. Methods outline in this report can be applied to deposits globally.

Potassium-based geochronology, including the ⁴⁰Ar/³⁹Ar and K-Ar methods, provides critical constraints on the timing and duration of many events and processes in earth history. These methods assume that a key parameter, the fraction of potassium with a mass of 40, does not vary in some relevant materials. Some recent work has identified some variability in these materials. This work examines the effects of this variability on calculated K-Ar and ⁴⁰Ar/³⁹Ar ages.